arXiv subjects

E. G. Thomas

Publications and source records attributed to E. G. Thomas.

2 recordsLinked to original sources

arXiv2021

Spatial Variation in the Responses of the Surface External and Induced Magnetic Field to the Solar Wind

We analyze the spatial variation in the response of the surface geomagnetic field (or the equivalent ionospheric current) to variations in the solar wind. Specifically, we regress a reanalysis of surface external and induced magnetic field (SEIMF) variations onto measurements of the solar wind. The regression is performed in monthly sets, independently for 559 regularly spaced locations covering the entire northern polar region above 50 magnetic latitude. At each location, we find the lag applied to the solar wind data that maximizes the correlation with the SEIMF. The resulting spatial maps of these independent lags and regression coefficients provide a model of the localized SEIMF response to variations in the solar wind, which we call «Spatial Information from Distributed Exogenous Regression.» We find that the lag and regression coefficients vary systematically with ionospheric region, season, and solar wind driver. In the polar cap region the SEIMF is best described by the (B$_{y}$) component of the interplanetary magnetic field (50-75% of total variance explained) at a lag the SEIMF is best described by the solar wind that varies with season and magnetic local time (MLT), from $\sim$15-20 min for dayside and afternoon MLT (except in Oct-Dec) to typically 30-40 min for nightside and morning MLT and even longer (60-65 min) around midnight MLT.

physics.space-ph↗

arXiv2020

Separation and Quantification of Ionospheric Convection Sources: 2. The Dipole Tilt Angle Influence on Reverse Convection Cells During Northward IMF

This paper investigates the influence of Earth's dipole tilt angle on the reverse convection cells (sometimes referred to as lobe cells) in the Northern Hemisphere ionosphere during northward IMF, which we relate to high-latitude reconnection. Super Dual Auroral Radar Network plasma drift observations in 2010-2016 are used to quantify the ionospheric convection. A novel technique based on Spherical Elementary Convection Systems (SECS) that was presented in our companion paper (Reistad et al., 2019, https://doi.org/10.1029/2019JA026634) is used to isolate and quantify the reverse convection cells. We find that the dipole tilt angle has a linear influence on the reverse cell potential. In the Northern Hemisphere the reverse cell potential is typically two times higher in summer than in winter. This change is interpreted as the change in interplanetary magnetic field-lobe reconnection rate due to the orientation of the dipole tilt. Hence, the dipole tilt influence on reverse ionospheric convection can be a significant modification of the more known influence from v(O$_{sw}$)B(O$_{z}$). These results could be adopted by the scientific community as key input parameters for lobe reconnection coupling functions.

physics.space-ph↗